1. Field of the Invention
The present invention relates to a block copolymer having a specific halogen-containing functional group, and a process for producing the block copolymer and a resin composition containing the block copolymer.
2. Related Art of the Invention
It has been known that block copolymers having a polymer block primarily comprising isobutylene and a polymer block primarily comprising vinylic aromatic hydrocarbons such as styrene show excellent performance in terms of barrier properties such as oxygen barrier properties. It has been known that various properties of thermoplastic resins, such as impact resistance, can be improved by blending the block copolymers into the thermoplastic resins, and therefore, the block copolymers are useful as resin modifiers (European Patent Application Publication No. 572,667).
Furthermore, block copolymers having an isobutylene-based polymer block and a styrenic polymer block as described above are lithiated and are then subjected to a reaction with carbon dioxide, whereby carboxyl groups can be added to a part of the styrene units. The block copolymers containing carboxyl groups, thus produced, have been proposed as resin modifiers with more excellent performance (Japanese Patent Application Laid-open No. Hei 6-287255).
Block copolymers having an ethylene-butylene-based copolymer block and a vinylic aromatic hydrocarbon-based polymer block are subjected to an addition reaction with unsaturated carboxylic acids such as acrylic acid and maleic anhydride in the presence of a radical generating agent, in order to add the functional groups to the copolymers, so that the carboxylic acid-type functional groups can readily be grafted to the ethylene-butylene-based copolymer block. However, block copolymers having an isobutylene-based polymer block and a vinylic aromatic hydrocarbon-based polymer block have poor radical reactivity because of the chemical structure of the isobutylene-based polymer block, and therefore, unsaturated carboxylic acids cannot be added to the block copolymers by such a method as described above. So as to yield a block copolymer having an isobutylene-based polymer block and a vinylic aromatic hydrocarbon-based polymer block and having a carboxylic acid-type functional group, very laborious procedures are required, comprising preliminarily producing a non-functional block copolymer having an isobutylene-based polymer block and a vinylic aromatic hydrocarbon-based polymer block by given polymerization procedures, lithiating the resulting non-functional block copolymer, and subjecting the resulting lithiated polymer to a reaction with carbon dioxide.
Meanwhile, U.S. Reissued Patent No. 34, 640 describes in the specification that, through the sequence of isobutylene polymerization and the polymerization of a monomer mixture of p-methylstyrene and p-chlorostyrene by using a polymerization initiating system composed of a dicumyl ether compound and titanium tetrachloride, a triblock copolymer can be recovered, having a structure such that copolymer blocks with p-methylstyrene and p-chlorostyrene are individually arranged on both the ends of the isobutylene polymer block. According to the procedures, the present inventors have produced a block copolymer having an isobutylene-based polymer block and a vinylic aromatic hydrocarbon-based polymer block and having a unit derived from p-chlorostyrene, and the inventors have further examined the application of the block copolymer as a resin modifier. However, the modification effects are not so significantly different from the modification effects of block copolymers with no p-chlorostyrene unit contained therein, or rather, the effects of the present block copolymer are sometimes poorer.